1. Field of the Invention
The present invention relates in general to a traffic signal light device, and more in particular to the traffic signal light device using high power Light-Emitting Diodes (LEDs).
2. Description of the Related Art
Light-Emitting Diodes (LEDs) have been used in many applications to replace the conventional incandescent lamps, fluorescent lamps, Neon tube and fiber optics light sources to reduce electrical cost, maintenance cost and increase reliability. Due to the fact that LEDs consume less electrical energy than conventional light sources while exhibiting much longer lifetime, many designs have been invented for various applications, such as traffic signal lights, channel letters, conventional illuminated commercial signs, street lights and street signs.
Recent advancements of high power LED technology enable additional applications over the conventional 5 mm (T1-¾) LEDs because of its higher light output efficiency and lower cost. However, for certain applications, such as traffic signal lights, the use of high power LEDs have been somewhat hampered because their light distribution pattern is not readily compatible with the asymmetric light distribution pattern required for traffic signal lights.
When high power LEDs are used for traffic signal applications, a Fresnel lens, as well as a spreading lens with a specific optical design, are used to distribute the light to meet the required specifications, such as the design by Keuperand Van Hees (U.S. Pat. No. 5,947,587) and by Wu, et al (U.S. Pat. No. 6,911,915). Besides the fact that the light emission pattern from the high power LEDs is symmetrical, the product designs in almost all cases center the light engine around the physical center of the device. This presents some difficulties in meeting the light distribution specifications which in general are non-symmetrical. In addition, placing the light engine around the center of the device in many cases presents some physical constraints on placing other components needed for the device.